John Snow, M.D. (1813--1858), a historical figure in epidemiology, provided one of the earliest examples of using epidemiologic methods to identify risk for disease and recommend preventive action.
On August 31, 1854, London experienced a recurrent epidemic of cholera and Snow suspected water from the Broad Street pump as the source of disease. Snow reviewed death records of area residents who died from cholera and documented that most of the deceased had lived near and drunk water from the pump. Snow presented his findings to community leaders, and the pump handle was removed on September 8, 1854.
Removal of the handle prevented additional cholera deaths, supporting Snow's theory that cholera was a waterborne, contagious disease. Snow's studies and the removal of the pump handle became a model for modern epidemiology and is considered to be a symbol of the importance of public health.
Today, many take a public health professional's oath, or the "Pump Handle" oath, to affirm or reaffirm their commitment to the field of public health.